The cycles of vaginal microbes

Rachel Tompa

The human vagina is colonized by a mixture of different bacteria, including a few Lactobacillus species in healthy women. A shift towards more species of bacteria is associated with the common infection bacterial vaginosis (BV). While the bacteria that cause BV have been characterized, and treatments exist, the short-term fluctuations of the vaginal bacterial community are not well understood. Relapse after BV treatment is common, and previous studies had not determined whether antibiotics are able to completely eradicate the offending microbes. To evaluate the rise and fall in vaginal bacteria in healthy women and women with BV, researchers led by VIDI associate member Dr. David Fredricks and VIDI postdoctoral fellow Dr. Sujatha Srinivasan used sensitive molecular detection techniques to track the levels of bacterial DNA of women over time.

The scientists asked the women to take daily vaginal samples for one to two weeks, and less frequently for up to four months; they tested each swab for 14 different types of vaginal bacteria. Their analysis included 14 healthy women, and eight with BV who were given antibiotics. They found that bacterial levels showed considerable variation over time even in healthy women, and that one bacterial species in particular, Gardnerella vaginalis, increased greatly in concentration during menstruation, perhaps due to an increased amount of iron. They also found that BV-associated bacteria declined dramatically following antibiotic treatment, so recurrence of BV is likely due to re-growth of the bacteria, not a failure of the original treatment. These findings imply that restarting antibiotic treatment may be the best course of action to address the high rate of relapse in this common condition.